1. Field of the Invention
This invention relates to well drilling operations and, more particularly, to a device for assisting in the assembly of pipe strings, such as casing strings, drill strings and the like; and/or to a device for measuring drilling parameters during a drilling operation.
2. Description of the Related Art
The drilling of oil wells involves assembling drill strings and casing strings, each of which comprises a plurality of elongated, heavy pipe segments extending downwardly from an oil drilling rig into a hole. The pipe string consists of a number of sections of pipe which are threadedly engaged together, with the lowest segment (i.e., the one extending the furthest into the hole) carrying a drill bit at its lower end. Typically, the casing string is provided around the drill string to line the well bore after drilling the hole and to ensure the integrity of the hole. The casing string also consists of a plurality of pipe segments which are threadedly coupled together and formed with internal diameters sized to receive the drill string and/or other pipe strings.
The conventional manner in which plural casing segments are coupled together to form a casing string is a labor-intensive method involving the use of a “stabber” and casing tongs. The stabber is manually controlled to insert a segment of casing into the upper end of the existing casing string, and the tongs are designed to engage and rotate the segment to threadedly connect it to the casing string. While such a method is effective, it is cumbersome and relatively inefficient because the procedure is done manually. In addition, the casing tongs require a casing crew to properly engage the segment of casing and to couple the segment to the casing string. Thus, such a method is relatively labor-intensive and therefore costly. Furthermore, using casing tongs requires the setting up of scaffolding or other like structures, and is therefore inefficient.
Accordingly, it will be apparent to those skilled in the art that there continues to be a need for a device for use in a drilling system which utilizes an existing top drive assembly to efficiently assemble pipe strings, and which positively engages a pipe segment to ensure proper coupling of the pipe segment to a pipe string.
Another problem associated with the drilling of oil wells includes the difficulties associated with accurately measuring drilling parameters in the oil and gas well system during a drilling operation, such as pipe string weight, torque, vibration, speed of rotation, angular position, number of revolutions, rate of penetration, and internal pressure. Current methods of measuring and observing such drilling parameters are generally indirect, meaning that they are measured at a point conveniently accessible but not necessarily located on the actual pipe sting.
For example, the pipe string weight is often indirectly measured by measuring the pull on a cable of a hoisting system, which raises and lowers the pipe string. This type of measurement is inaccurate due to frictional forces associated with the cable, the sheaves, and the measurement device attached to the cable.
The pipe string torque is difficult to measure since it is often difficult to measure the torque output of the torque driving system, which rotates or drives the pipe string. For example, typically, the pipe string is either rotated with a large mechanical drive called a rotary table or directly by a large motor called a top drive. The torque output of each of these drive systems cannot be easily measured and most often is either calculated from the current going to the drive motor when a top drive is used, or by measuring the tension of a drive chain which drives the rotary table when a rotary table is used. Both of these methods are very inaccurate and subject to outside influences that can cause the readings to be inconsistent, such as stray electrical currents through the drive motor when a top drive is used, or wear of the measured mechanical devices when a rotary table is used.
Another drilling parameter that is difficult to measure is vibration. Vibration of the pipe string is very damaging to its components especially to the drill bit at the end of the pipe string, which drills a well bore.
Various methods have been proposed to solve the above described problems with the measuring of drilling parameters during a drilling operation, including installing various instrumented pins onto components of the hoisting system or the top drive system. Other more direct approaches have been tried with limited success. For example, some have installed a load sensor at the top of the derrick for measuring pull of the hoisting system on the derrick. These are commonly referred to as crown block weight sensors.
Various other devices have been developed for directly measuring torque and vibration on the pipe string. For example, one such device for use with a rotary table includes a plate that attaches to the top of the rotary table between the table and a drive bushing, referred to as the kelly drive bushing. However, currently more and more oil and gas well drilling systems are using top drive drilling systems instead of rotary tables, rending this approach less desirable and possibly obsolete.
Others have tried to make special instrumented subs that screw directly into the pipe string. One such device is large and bulky and does not fit into existing top drive systems. These devices provide the accuracy desired in the measure of the drilling parameters, but compromise the drilling equipment due to their size and shape. In addition, these devices require redesign of the top drive system to accommodate them.
Accordingly, a need exists for an apparatus and method for accurately measuring drilling parameters during a drilling operation that does not require modification of the top drive assembly to which it attaches. The present invention addresses these needs and others.